Various methods of making perforated polymer films are known. For example, U.S. Pat. No. 3,012,918 (Schaar), and British Patent Specification Nos. GB 851,053 and GB 854,473 all generally describe processes and apparatuses for improving the heat-sealability of polymeric films by passing the film over a cooled, hollow, rotating, metal cylinder or support roll with a desired perforation pattern while a jet of gas-heated air is directed onto the surface of the film so that specific areas of the film are melted, forming a pattern of perforations.
U.S. Pat. No. 3,394,211 (MacDuff) discusses flame perforation of heat-shrinkable, biaxially oriented polypropylene films. British Patent Specification No. GB 1,012,963 and GB 1,073,605 disclose methods and apparatuses for flame perforating suitable thermoplastic films capable of being softened and melted by heat.
Oxygen-enriched flames have been used to improve the wettability or adhesion properties of polymer films. Such uses are disclosed in patent literature that includes U.S. Pat. Nos. 3,153,683; 3,255,034; 3,347,697; 3,361,607; 3,375,126; 3,431,135; 3,783,062; and 4,622,237 and 5,891,967. These patents describe the use of oxygen-enriched flames for the surface modification of polymers.